南秦岭志留系铅锌矿床中硅质岩岩石学及地球化学

南秦岭泥盆系内产出的众多矿床中含有层纹条带状硅质岩-硅质板岩,对其成因的研究有助于查明矿床成因和确定区域找矿方向.研究表明,硅质岩化学成分纯净,SiO2含量多在90%以上.硅质岩中大部分微量元素含量低于地壳克拉克值,但富集Zn、Pb、As、Sb、Ag;硅质岩的Fe-Mn-(Cu+Ni+Co)×10图解表明硅质岩具热水沉积性质.硅质岩与矿石两者的稀土元素特点相似,具有ΣREE低(44.52×10-6)、轻重稀土分异较明显(LREE/HREE=6.51)、北美页岩标准化配分曲线呈平缓趋势、铈负异常不明显(δCe值为0.97)和铕正异常明显(δEu值为1.42)的特点;硅质岩的δ30Si为-0.5‰～0.0‰,δ18O为17.8‰～19.9‰,硅、氧同位素组成及形成温度(84～101℃)也暗示它为海底热水沉积成因.     

Cordierite-bearing granulites from Ihosy,southern Madagascar:Petrology,geochronology and regional correlation of suture zones in Madagascar and India

Madagascar,a major fragment of Gondwana,is mainly composed of Precambrian basenent rocks formed by Mesoarchean to Neoproterozoic tectono-thernial events and recording a Pan-African metamorphic overprint.The Ranotsara Shear Zone in southern Madagascar has been correlated with shear zones in southern India and eastern Africa in the reconstruction of the Gondwana supercontinent.Here we present detailed petrology,mineral chemistry,metamorphic P-T constraints using phase equilibrium modelling and zircon U-Pb geochronological data on high-grade metamorphic rocks from Ihosy within the Ranotsara Shear Zone.Garnet-cordierite gneiss from Ihosy experienced two stages of metamorphism.The peak mineral assemblage is interpreted as garnet+sillimanite+cordierite+quartz+plagioclase+Kfeldspar+magnetite+spinel+ilmenite,which is overprinted by a retrograde mineral assemblage of biotite+garnet+cordierite+quartz+plagioclase+K-feldspar+magnetite+spinel+ilmenite.Phase equilibria nodelling in the system Na_2 O-CaO-K_2 O-FeO-MgO-Al_2 O_3-SiO_2-H_2 O-TiO_2-Fe_2 O_3(NCKFMASHTO) indicates peak metamorphic conditions of 850-960 C and 6.9-77 kbar,and retrograde P-Tconditions of 740 C and 4.8 kbar,that define a clockwise P-T path.Near-concordant ages of detrital zircon grains in the garnet-cordierite gneiss dominantly exhibit ages between 2030 Ma and 1784 Ma,indicating dominantly Paleoproterozoic sources.The lower intercept age of 514±33 Ma probably indicates the timing of high-grade metamorphism,which coincides with the assembly of the Gondwana supercontinent.The comparable rock types,zircon ages and metamorphic P-T paths between the Ranotsara Shear Zone and the Achankovil Suture Zone in southern India support an interpretation that the Ranotsara Shear Zone is a continuation of the Achankovil Suture Zone.     

Dating of detrital zircons from the Dabure clastic rocks: the discovery of Neoproterozoic strata in southern Qiangtang,Tibet

ABSTRACT

This article reports the results of field mapping and the petrology of clastic rocks in the Dabure area, southern Qiangtang, Tibet, together with the results of U–Pb dating of detrital zircons from these rocks. The Dabure clastic rocks are characterized by low compositional and textural maturity, and they have been affected by lower greenschist facies metamorphism. The deposits exhibit the typical features of turbidites. Altogether, 279 detrital zircons were selected for U–Pb dating, and the ages fall into five groups: 550–650, ~800, 900–1100, 1600–1800, and 2300–2500 Ma. In general, the ages of the detrital zircons that are older than ~550 Ma are similar to those found elsewhere in the southern Qiangtang and Himalayan terranes. The most reliable youngest age of a detrital zircon from the Dabure clastic rocks is ~550 Ma. In the southern part of the Tibet Plateau, strata with the same ages and lithologies as the Dabure clastic rocks are widespread, especially in the Himalayan terrane. Combining our data with previous work on the basalts in the Dabure area (the Dabure basalts), we tentatively suggest that the Dabure clastic rocks represent the late Ediacaran (~550 Ma) sedimentary record for the Qiangtang terrane, and that before the late Neoproterozoic the southern Qiangtang terrane was possibly connected to the Himalayan terrane.     

Petrology of Karoo volcanic rocks in the southern Lebombo monocline, Mozambique

The Karoo volcanic sequence in the southern Lebombo monocline in Mozambique contains different silicic units in the form of pyroclastic rocks, and two different basalt types. The silicic units in the lower part of the Lebombo sequence are formed by a lower unit of dacites and rhyolites (67–80 wt.% SiO₂) with high Ba (990–2500 ppm), Zr (800–1100 ppm) and Y (130–240 ppm), which are part of the Jozini–Mbuluzi Formation, followed by a second unit, interlayered with the Movene basalts, of high-SiO₂ rhyolites (76–78 wt.%; the Sica Beds Formation), with low Sr (19–54 ppm), Zr (340–480 ppm) and Ba (330–850 ppm) plus rare quartz-trachytes (64–66 wt.% SiO₂), with high Nb and Rb contents (240–250 and 370–381 ppm, respectively), and relatively low Zr (450–460 ppm). The mafic rocks found at the top of the sequence are basalts and ferrobasalts belonging to the Movene Formation. The basalts have roughly flat mantle-normalized incompatible element patterns, with abundances of the most incompatible elements not higher than 25 times primitive mantle. The ferrobasalt has TiO₂  4.7 wt.%, Fe₂O_3t = 16 wt.%, and high Y (100 ppm), Zr (420 ppm) and Ba (1000 ppm). The Movene basalts have initial (at 180 Ma) ⁸⁷Sr/⁸⁶Sr = 0.7052–0.7054 and ¹⁴³Nd/¹⁴⁴Nd = 0.51232, and the Movene ferrobasalt has even lower ⁸⁷Sr/⁸⁶Sr (0.70377) and higher ¹⁴³Nd/¹⁴⁴Nd (0.51259). The silicic rocks show a modest range of initial Sr-(⁸⁷Sr/⁸⁶Sr = 0.70470–0.70648) and Nd-(¹⁴³Nd/¹⁴⁴Nd = 0.51223–0.51243) isotope ratios. The less evolved dacites could have been formed after crystal fractionation of oxide-rich gabbroic cumulates from mafic parental magmas, whereas the most silica-rich rhyolites could have been formed after fractional crystallization of feldspars, pyroxenes, oxides, zircon and apatite from a parental dacite magma. The composition of the Movene basalts imply different feeding systems from those of the underlying Sabie River basalts.     

Petrology of amphibolite-facies mafic and ultramafic rocks from the Catalina Schist, southern California: metasomatism and migmatization in a subduction zone metamorphic setting

Abstract The Catalina Schist of southern California is a subduction zone metamorphic terrane. It consists of three tectonic units of amphibolite-, high- P greenschist- and blueschist-facies rocks that are structurally juxtaposed across faults, forming an apparent inverted metamorphic gradient. Migmatitic and non-migmatitic metabasite blocks surrounded by a meta-ultramafic matrix comprise the upper part of the Catalina amphibolite unit. Fluid-rock interaction at high- P , high- T conditions caused partial melting of migmatitic blocks, metasomatic exchange between metabasite blocks and ultramafic rocks, infiltration of silica into ultramafic rocks, and loss of an albitic component from nonmigmatitic, clinopyroxene-bearing metabasite blocks.
Partial melting took place at an estimated P =˜8–11 kbar and T =˜640–750°C at high H₂O activity. The melting reaction probably involved plagioclase + quartz. Trondhjemitic melts were produced and are preserved as leucocratic regions in migmatitic blocks and as pegmatitic dikes that cut ultramafic rocks.
The metasomatic and melting processes reflected in these rocks could be analogous to those proposed for fluid and melt transfer of components from a subducting slab to the mantle wedge. Aqueous fluids rather than melts seem to have accomplished the bulk of mass transfer within the mafic and ultramafic complex.     

Petrology of gedrite-bearing rocks in mid-crustal ductile shear zones from the Eastern Ghats Belt, India

A suite of metapelitic, basic and quartzofeldspathic rocks intruded by enderbitic gneiss from the southernmost tip of the Eastern Ghats Belt, India, and metamorphosed at c. 750–800  °C, 6  kbar, were subjected to repeated ductile shear deformation, hydration, cooling and accompanying alkali metasomatism along narrow shear zones. Gedrite-bearing assemblages developed in the shear zones traversing metapelitic rocks. Interpretation of the reaction textures in an appropriate P–T  grid in the system FMASH, an isothermal–isobaric μ _H2O– μ _Na2O grid in the system NFMASH, and geothermobarometric data suggest a complex evolutionary history for the gedrite-bearing parageneses. Initially, gedrite-bearing assemblages were produced due to increase in μ _Na2O at nearly constant but high μ _H2O accompanying cooling. Gedrite was partially destabilized to orthopyroxene+albite due to progressively increasing μ _Na2O. During further cooling and at increased μ _H2O a second generation of gedrite appeared in the rocks.     

青海尕林格南地区火山岩地球化学特征及锆石U-Pb年龄

在东昆仑山脉西段祁漫塔格山中东部的尕林格南地区发育一套火山岩,调查显示火山活动爆发相→溢流相相间的韵律周期较明显,见由玄武质含火山角砾凝灰岩→玄武岩、玄武质凝灰岩→安山岩、安山质角砾凝灰岩→安山岩,以及安山质含火山角砾凝灰岩和安山岩质凝灰岩→玄武岩组成的4个韵律。根据研究区安山质火山角砾凝灰岩的LA-ICP-MS锆石U-Pb年龄222.2±2.1Ma,将该火山岩地层由前人划分的顶志留统—下泥盆统契盖苏组火山岩段重新厘定为上三叠统鄂拉山组。岩石地球化学研究结果表明,该套火山岩属于亚碱性钙碱性系列岩石,具有富钾、同源岩浆演化的特点,并具弧火山岩和碰撞火山岩的地球化学特征,为陆内造山作用下的产物,较好地记录了东昆仑祁漫塔格造山带在晚三叠世岩浆演化的地质信息。     

南祁连土尔根达坂巴龙贡噶尔组火山岩地球化学及锆石U-Pb年代学研究

广泛分布于南祁连的志留纪巴龙贡噶尔组的形成时代和构造归属存在很大分歧,为了说明土尔根达坂巴龙贡噶尔组英安岩-流纹岩形成时代及地质意义,本文选择代表性岩石进行了主微量元素和LA-ICP-MS锆石U-Pb年代学分析。地球化学结果表明,巴龙贡噶尔组火山岩为高钾钙碱性过铝质岩石,在成岩过程中经历了一定的结晶分异作用。火山岩微量元素表现出不同程度的富集K、Pb和轻稀土元素(LREE),相对亏损高场强元素(HFSE)Zr、Ce、Nb,具有明显的P、Ti负异常。LREE/HREE之比为6.98～10.13,δEu介于0.40～0.54显示负异常,表明稀土元素分馏明显;各样品稀土曲线具有相似的右倾型配分模式,反映为同源岩浆产物。三个样品LA-ICP-MS锆石U-Pb谐和年龄分别为438.1±2.2Ma, 403.0±2.6Ma, 404.9±2.8Ma,说明火山岩的形成地质时期为早志留世-早泥盆世。综合对比得出原志留纪巴龙贡噶尔组应进行解体及重新认识,土尔根达坂地区巴龙贡噶尔组火山活动与南部柴达木花岗岩岩浆活动近于同期,两者可能都与柴达木陆块与中南祁连板块碰撞造山带上不同块体之间的伸展、滑塌等一系列岩...     

藏南羊卓雍错南部桑秀组火山岩的特征及构造环境

羊卓雍错南部桑秀组中分布有由玄武岩-安山岩-英安岩构成的海相火山岩组合，区域露头上玄武岩占绝对优势，喷发时代为晚侏罗世晚期-早白垩世早期。区域资料显示，这一时期该地区处于冈瓦纳大陆的被动陆缘。地球化学特征表明，本区火山岩与洋脊玄武岩和洋岛型玄武岩有明显区别，显示大陆拉张带或大陆裂谷亚碱性拉斑玄武岩的特征。     

Early Cretaceous granitic rocks from the southern Jiaodong Peninsula,eastern China: implications for lithospheric extension

ABSTRACT

Zircon U–Pb ages, major element and trace element compositions, and Sr, Nd, and Pb isotopic compositions for late Mesozoic granites from the southern Jiaodong Peninsula (eastern China) were determined. Ages for the Wulianshan, Xiaozhushan, and Dazhushan plutons are 119.1–122.3, 114.2, and 108.9 Ma, respectively. Major and trace element characteristics show that these granitic rocks belong to alkaline, A-type granites formed in an extensional setting. Trace element compositions show strong, variable negative anomalies in Ba, K, P and Ti, and positive anomalies in Rb, Th, U, Pb, Ce, Zr, and Hf, which are typical characteristics of A-type granites. Variable Sr and Nd isotopic compositions, ⁸⁷Sr/⁸⁶Sr(i) = 0.70540–0.7071 and εNd(t) = ?14.5 to ?20.9. Whole-rock Pb isotopic compositions have the following ranges, (²⁰⁶Pb/²⁰⁴Pb)t = 15.707–16.561, (²⁰⁷Pb/²⁰⁴Pb)t = 15.376–16.462, and (²⁰⁸Pb/²⁰⁴Pb)t = 36.324 to 37.064. Isotopic modelling indicates an origin that lies between mantle tapped by Cenozoic basalts around the Tan-Lu megafault and lower continental crust (LCC), and which can be explained by mixing of 11–18% mantle and 82–89% LCC. Based on new and compiled data, we suggest that the southern Jiaodong Peninsula, as well as the Laoshan area, was in a regional extensional setting of an orogenic belt during 106–126 Ma. The granitic rocks may be the result of late Mesozoic lithospheric thinning and decratonization (i.e. late Mesozoic craton destruction event occurring throughout eastern China).     

南羌塘侏罗纪盆地的沉积－构造转换与烃源岩

沉积盆地层序地层和岩相古地理研究以及沉积-构造转换过程分析，是探讨沉积体系时空演化的重要思路。通过沉积-构造转换的分析。指出羌南地区在侏罗纪经历了从被动大陆边缘到夭折前陆，最后隆升剥蚀的演化历史；初步厘定了南羌塘地区烃源岩形成环境。在经历4次海侵的过程中。相应发育了两个陆源碎屑岩-碳酸盐岩沉积旋回。在这4次沉积-构造转换过程中．发育3套黑色页岩沉积：分别属于被动大陆边缘烃源岩和前陆盆地两个阶段烃源岩。是南羌塘侏罗纪盆地的油气评价的物质基础。     

阿尔泰诺尔特地区泥盆纪正格河火山岩的厘定及其地质意义

阿勒泰南缘诺尔特地区晚古生代火山岩十分发育,其中正格河一带出露一套片理化蚀变流纹岩与含凝灰质英安流纹岩的岩石组合,呈北西-南东向带状展布,前人将其划为石炭纪红山嘴组a段。本次工作对其进行的LAICPMS锆石U-Pb测年结果显示为早泥盆世(206Pb/238U加权平均年龄值为(400.4±3.6)Ma),时代不同于红山嘴组所属的石炭纪。其岩性明显区别于红山嘴组b、c段地层,且稳定成规模出露,故对此套流纹岩组合进行了重新厘定,暂命名为正格河火山岩。岩石Si O2含量在69.77%~75.16%,里特曼指数为1.26~1.70,(Na2O+K2O)介于5.90%~7.28%,A/CNK值介于0.88~1.16,显示钙碱性、偏铝质岩石特征。微量元素富集Rb、Th等大离子亲石元素,亏损Nb、Ta、Hf等高场强元素,稀土元素总量变化较大,∑REE介于189.20×10-6~308.47×10-6,轻、重稀土元素分馏较强((La/Yb)N=5.82~7.86),铕负异常(δEu=0.45~0.75),具有与俯冲作用有关的岩浆作用特征。结合区域地质资料,表明正格河火山岩形成于活动大陆边缘构造环境。     

Petrology of ultrahigh-pressure rocks from the southern Su-Lu region, eastern China

Abstract In the Su-Lu ultrahigh- P terrane, eastern China, many coesite-bearing eclogite pods and layers within biotite gneiss occur together with interlayered metasediments now represented by garnet-quartz-jadeite rock and kyanite quartzite. In addition to garnet + omphacite + rutile + coesite, other peak-stage minerals in some eclogites include kyanite, phengite, epidote, zoisite, talc, nyböite and high-Al titanite. The garnet-quartz-jadeite rock and kyanite quartzite contain jadeite + quartz + garnet + rutile ± zoisite ± apatite and quartz + kyanite + garnet + epidote + phengite + rutile ± omphacite assemblages, respectively. Coesite and quartz pseudomorphs after coesite occur as inclusions in garnet, omphacite, jadeite, kyanite and epidote from both eclogites and metasediments. Study of major elements indicates that the protolith of the garnet-quartz jadeite rock and the kyanite quartzite was supracrustal sediments. Most eclogites have basaltic composition; some have experienced variable 'crustal'contamination or metasomatism, and others may have had a basaltic tuff or pyroclastic rock protolith.
The Su-Lu ultrahigh- P rocks have been subjected to multi-stage recrystallization and exhibit a clockwise P-T path. Inclusion assemblages within garnet record a pre-eclogite epidote amphibolite facies metamorphic event. Ultrahigh- P peak metamorphism took place at 700–890° C and P >28 kbar at c . 210–230 Ma. The symplectitic assemblage plagioclase + hornblende ± epidote ± biotite + titanite implies amphibolite facies retrogressive metamorphism during exhumation at c . 180–200 Ma. Metasedimentary and metamafic lithologies have similar P-T paths. Several lines of evidence indicate that the supracrustal rocks were subducted to mantle depths and experienced in-situ ultrahigh- P metamorphism during the Triassic collision between the Sino-Korean and Yangtze cratons.     

Gem corundum deposits of Madagascar: A review

Madagascar is one of the most important gem-producing countries in the world, including ruby and sapphires. Gem corundum deposits formed at different stages in the geological evolution of the island and in contrasting environments. Four main settings are identified: (1) Gem corundum formed in the Precambrian basement within the Neoproterozoic terranes of southern Madagascar, and in the volcano-sedimentary series of Beforona, north of Antananarivo. In the south, high-temperature (700 to 800 °C) and low-pressure (4 to 5 kbar) granulites contain deposits formed during the Pan-African orogenesis between 565 and 490 Ma. They accompany mafic and ultramafic complexes (ruby deposits of the Vohibory group), skarns at the contact between Anosyan granites and the Proterozoic Tranomaro group (sapphire deposits of the Tranomaro–Andranondambo district), and shear-zone corridors cross-cutting feldspathic gneisses, cordieritites and clinopyroxenites in the Tranomaro, Vohimena and Androyan metamorphic series (biotite schist deposits of Sahambano and Zazafotsy, cordieritites of Iankaroka and Ambatomena). The circulation of fluids, especially along discontinuities, allowed in-situ alkaline metasomatism, forming corundum host rocks related to desilicified granites, biotitites, “sakenites” and “corundumites”. (2) Gem corundum also occurs in the Triassic detrital formations of the Isalo group, as giant palaeoplacers in the Ilakaka–Sakaraha area. Here, sapphires and rubies may come from the metamorphic granulitic terranes of southern Madagascar. (3) Gem corundum deposits occur within the Neogene-Quaternary alkali basalts from Ankaratra (Antsirabe–Antanifotsy area) and in the Ambohitra Province (Nosy Be, Ambato and Ambondromifehy districts). Primary deposits are rare, except at Soamiakatra where ruby in gabbroic and clinopyroxenite xenoliths within alkali-basalts probably derive from mantle garnet peridotites. The blue-green-yellow sapphires typical of basaltic fields are always recovered in palaeoplacer (in karst formed upon Jurassic limestones from the Montagne d'Ambre, Antsiranana Province) and alluvial and soil placers (Ankaratra volcanic massif). (4) Deposits occur within Quaternary eluvial, colluvial and alluvial concentrations, such as high-quality rubies from the Andilamena and Vatomandry deposits.     

Role of H2O in the formation of garnet coronas during near‐isobaric cooling of mafic granulites: the Tasiusarsuaq terrane,southern West Greenland

The Mesoarchaean Tasiusarsuaq terrane of southern West Greenland consists of Tonalite–trondhjemite–granodiorite gneisses and, locally, polymetamorphic mafic and ultramafic rocks. The terrane experienced medium‐pressure granulite facies conditions during M_1A in the Neoarchean, resulting in the development of two‐pyroxene melanosome assemblages in mafic granulites containing garnet‐bearing leucosome. Reworking of these rocks during retrogression introduced garnet to the melanosome in the form of overgrowths, coronas and grain necklaces that separate the mafic minerals from plagioclase. NCFMASHTO pseudosection modelling constrains the peak metamorphism during M_1A to ～850 °C and 7.5 kbar at fluid‐saturated conditions. Following M_1A, the rocks retained their M_1A H₂O content and became fluid‐undersaturated as they underwent near‐isobaric cooling to ～700 °C and 6.5–7 kbar, prior to reworking during M_1B. These low H₂O contents allowed for the formation of garnet overgrowths and coronas during M_1B. The stability of garnet is greatly increased to lower pressure and temperature in fluid‐absent, fluid‐undersaturated mafic rocks, indicating that fluid and melt loss during initial granulite facies metamorphism is essential for the introduction of garnet, and the formation of garnet coronas, during retrogression. The occurrence of garnet coronas is consistent with, but not unique to, near‐isobaric cooling paths.     

Structural and remote sensing studies of the southern Betsimisaraka Suture, Madagascar

An assessment of the southern Betsimisaraka Suture (B.S.) of southeastern Madagascar using remote sensing and field investigation reveals a complex deformation history. Image processing of Landsat ETM+data and JERS-I Synthetic Aperture Radar (SAR) imagery was integrated with field observations of structural geology and field petrography. The southern B.S. divides the Precambrian basement rocks of Madagascar in two parts. The western part includes Proterozoic rocks whereas the eastern part is an Archean block, named the Masora block. The southern part of the B.S. includes high-grade metamorphic rocks, recording strong deformation and has mineral deposits including chromite, nickel, and emerald, characteristic of oceanic material that is compatible with a suture zone.Large-scale structural features indicate ductile deformation including three generations of folding (F1, F2, and F3) associated with dextral shearing. The first folding event (F1) shows a succession of folds with NE striking axial planes. The second folding event (F2) mainly has north–south striking axial planes and the last event (F3) is represented by mega folds that have ENE–WSW axial plane directions and have NNW and SSE contractional strain patterns. Closure of the Mozambique Ocean between two components of Gondwana sandwiched rocks of the B.S. and formed upright folds and shortening zones which produced N–S trending lineaments. Later dextral movements followed the contraction and formed NW–SE trending lineaments and N–S trending normal faults associated with dextral strike slip faults and fractures.     

Cretaceous climate oscillations in the southern palaeolatitudes: New stable isotope evidence from India and Madagascar

Palaeotemperatures for the Cretaceous of India and Madagascar have been determined on the basis of oxygen isotopic analysis of well-preserved Albian belemnite rostra and Maastrichtian bivalve shells of from the Trichinopoly district, southern India, and Albian nautiloid and ammonoid cephalopods from the Mahajang Province, Madagascar. The Albian (possibly late Albian) palaeotemperatures for Trichinopoly district are inferred to range from 14.9 °C to 18.5 °C for the epipelagic zone, and from 14.3 °C to 15.9 °C for the mesopelagic zone, based on analyses of 65 samples; isotopic palaeotemperatures interpreted as summer and winter values for near-bottom shelf waters in this area fluctuate from 16.3 to 18.5 °C and from 14.9 to 16.1 °C, respectively. The mentioned palaeotemperatures are very similar to those calculated from isotopic composition of middle Albian belemnites of the middle latitude area of Pas-de-Calais in Northern hemisphere but significantly higher than those calculated from isotopic composition of Albian belemnites from southern Argentina and the Antarctic and middle Albian belemnites of Australia located within the warm-temperate climatic zone. Isotopic analysis of early Albian cephalopods from Madagascar shows somewhat higher palaeotemperatures for summer near-bottom shelf waters in this area (20.2-21.6 °C) in comparison with late Albian palaeotemperatures calculated from southern India fossils, but similar winter values (13.3-16.4 °C); however, the latter values are somewhat higher than those calculated from early Albian ammonoids of the tropical-subtropical climatic zone of the high latitude area of southern Alaska and the Koryak Upland. The new isotopic palaeotemperature data suggest that southern India and Madagascar were located apparently in middle latitudes (within the tropical-subtropical climatic zone) during Albian time. In contrast to the Albian fossils, isotope results of well-preserved early Maastrichtian bivalve shells from the Ariyalur Group, Trichinopoly district, are characterised by lower δ¹⁸O values (up to −5.8‰) but normal δ¹³C values, which might be a result local freshwater input into the marine environment. Our data suggest that the early Maastrichtian palaeotemperature of the southern Indian near-bottom shelf waters was probably about 21.2 °C, and that this middle latitude region continued to be a part of tropical-subtropical climatic zone, but with tendency of increasing of humidity at the end of Cretaceous time.     

Phanerozoic upper crustal tectono-thermal development of basement rocks from central Madagascar: An integrated fission-track and structural study

An integrated study of fission-track (FT) dating and structural geology revealed a complex tectono-thermal history preserved in basement rocks of central Madagascar since the amalgamation of Gondwana at the end of the Cambrian. A detailed study of five domains argues for several cooling steps with associated brittle deformations during the separation of Madagascar.Titanite and apatite FT ages range between 483 Ma and 266 Ma and between 460 Ma and 79 Ma, respectively. The titanite FT data indicate that the final cooling after the latest metamorphic overprint was terminated at c. 500 Ma (FC1). A 150 Myr phase of minor cooling (SC2), possibly related to a phase of tectonic quiescence and isostatic compensation, followed episode FC1. Between the Carboniferous and Early Jurassic, when an intracontinental rift developed between East Africa and Madagascar, complex brittle deformation effected the western margin of Madagascar and led to differential cooling of small basement blocks (FC3–FC5). During this period, ductile structural trends were reactivated at the western basement margin and in the centre of the island.A Late Cretaceous thermal event (T1) affected apatite FT data of samples from western–central and the eastern margin of Madagascar. These ages are related to the Madagascar–India/Seychelles break-up, whereby the thermal penetration along the eastern coast was restricted to the west by the Angavo shear zone (AGSZ). The Cretaceous evolution of the eastern margin was associated with minor erosion and was triggered by vertical displacements along brittle structures.     

Geochemistry and petrogenesis of lamprophyric dykes and the associated rocks from Eslamy peninsula, NW Iran: Implications for deep-mantle metasomatism

Eslamy peninsula in NW of Iran is formed by a strato-volcano with collapsed calderon, which is intruded by lamprophyric dykes with minette composition. Also trachytic and microsyenitic dykes have intruded the volcanic rocks. The oldest volcanic activity includes eruption of leucite basanite, leucite tephrite, basanite and tephrite, which are associated with pyroclastic rocks. Lamprophyric dykes are distinguishable with large mica phenocrysts. Mica-clinopyroxenite xenoliths can be found in the rocks. The source magma of the rocks had a ultrapotassic to shoshonitic nature, rich in LREE and LILE. Eslamy peninsula lamprophyres are between alkaline and calc-alkaline lamprophyres in terms of REE patterns and spider diagrams for trace elements, but are closer to clac-alkaline lamprophyres. The behaviour of trace elements studied by the means of spider diagrams show that the magma, producing the lamprophyres, is generated from deep-mantle probably from a garnet-bearing source (garnet lherzolite) with high CO₂/H₂O content. The resulted magma had interacted with crustal materials and had formed Eslamy peninsula lamprophyres in a post-collisional tectonic setting. Geochemistry of rare elements indicate an extensive rutile-rich metasomatism in the source magma of the lamprophyres.     

浙江江山—龙游南部地区钾玄质侵入岩的厘定及其找矿意义

江山—龙游南部地区晚中生代侵入岩分布广泛,以往被认为是钙碱性系列岩石,笔者通过野外地质、岩石学和元素地球化学研究表明,石英二长岩、二长岩、正长岩以及与之伴生的花岗岩与花岗斑岩属钾玄质系列岩石。这套岩石高碱(Na2O K2O=7.80%～10.47%)、富钾(K2O/Na2O=0.92～1.91)、贫钛(TiO2=0.2%～0.88%)、Al2O3含量较高且变化范围大(11.08%～17.77%),富集大离子亲石元素(LILE)和轻稀土元素(LREE),且Ce/Yb(27.29～85.64)、Ta/Yb(0.42～0.73)和Th/Yb(3.44～14.44)比值高,具有钾玄质系列的岩石地球化学特征。该区矿产资源较为丰富,矿床在时间与空间上多与钾玄质侵入岩密切共生,钾玄质侵入岩为成矿母岩,是重要的找矿岩石学标志。